Evaluation of Changes in Human Corneas After Femtosecond Laser-Assisted LASIK and Small-Incision Lenticule Extraction (SMILE) Using Non-Contact Tonometry and Ultra-High-Speed Camera (Corvis ST)

Purpose: To evaluate theoretical biomechanical advantages of human corneas treated with small incision lenticule extraction (SMILE) compared with femtosecond laser-assisted LASIK (FS-LASIK)Patients and methods: In a prospective, comparative, non-randomized, consecutive case series patients with moderate to high myopia and/or astigmatism underwent corneal refractive surgery. Patients either received standard FS-LASIK or SMILE. Preoperatively and up to 3 months postoperatively data were analyzed including tomography with Pentacam HR, Goldmann tonometry, non-contact tonometry, and deformability of the cornea using an ultra-high-speed camera (Corvis ST). Data were analyzed and p < 0.05 was considered as statistically significant (t-test).Results: Seventy-three patients (128 eyes) were treated. Forty-eight eyes of 29 patients underwent FS-LASIK and 80 eyes of 44 patients underwent SMILE. Preoperative spherical equivalent (SE) was -3.23 1.64 D (FS-LASIK group) and -4.83 +/- 1.63 D (SMILE group) (p < 0.0001). Almost all parameters obtained by Corvis ST between preoperative and postoperative measurements showed significant changes after refractive surgery. Significant changes were seen between both groups postoperatively. However, matched pair subgroup analysis (n = 69; 26 eyes FS-LASIK; 43 eyes SMILE) of eyes with initially equal pachymetry, intraocular pressure, SE, and difference of pre- to postoperative pachymetry (p>0.05), showed no significant changes in parameters measured with Corvis ST (p>0.05).Conclusions: Corneal biomechanical parameters measured preoperatively with Corvis ST showed significant differences postoperatively in total and in both groups. In subgroup analysis with homogenous groups, FS-LASIK showed no significant changes in biomechanical data measured with Corvis ST compared with SMILE.